branching-logic-flow

name	branching-logic-flow
description	Prefer defaulting and naked switches over if/else chains for shallow branching logic in Go. Use when writing or refactoring conditional logic with 1-3 branches.

Branching Logic Flow

For shallow branching (1-3 cases), prefer defaulting or naked switches over if/else chains. This reduces nesting, avoids duplication, and lowers the cognitive load.

When to Apply

• Writing new conditional logic with 1-3 branches
• Refactoring nested if/else blocks
• Type assertions on any / map[string]any
• Any branching where each branch assigns to the same variable

Rule 1: Default first, override later

Initialize the variable with its default value, then override only in the special case.

❌ Avoid:

var result map[string]any
if outer, ok := input["outer"].(map[string]any); ok {
    if inner, ok := outer["inner"].(map[string]any); ok {
        result = make(map[string]any, len(inner))
        maps.Copy(result, inner)
    } else {
        result = make(map[string]any)
    }
} else {
    result = make(map[string]any)
}

✅ Prefer:

result := make(map[string]any)
if outer, ok := input["outer"].(map[string]any); ok {
    if inner, ok := outer["inner"].(map[string]any); ok {
        result = make(map[string]any, len(inner))
        maps.Copy(result, inner)
    }
}

Rule 2: Naked switch over if/else if/else ladders

❌ Avoid:

if a > b {
    result = a
} else if a == b {
    result = a + b
} else {
    result = b
}

✅ Prefer:

switch {
case a > b:
    result = a

case a == b:
    result = a + b

default:
    result = b
}

For simple two-way numeric comparisons, prefer the min/max built-ins (Go 1.21+):

result := max(a, b)

When NOT to Apply

• Default initialization is heavyweight (DB call, large allocation, external API)
• The "default" case is exceptional and should fail fast with an error
• Conditions are deeply nested (>3 levels) — extract to a separate function instead
• Defaulting could mask a bug that should be surfaced explicitly

Related Modern Go Patterns

• Use maps.Copy(dst, src) instead of manual copy loops (destination must be non-nil)
• Use cmp.Or(a, b, "default") to pick the first non-zero value across fallbacks
• Always use the two-value form v, ok := x.(T) for type assertions